Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Volcanic ash parent material, short-range-order minerals and Andosol carbon
Volcanic ash parent material, short-range-order minerals and Andosol carbon
Volcanic ash weathers quickly into poorly crystalline minerals such as allophane and ferrihydrite that bind organic matter and phosphate strongly, giving Andosols very high carbon storage and phosphorus fixation.
Boundary: where this process starts
Starts with: Fresh ash and tephra (volcanic glass) falls and weathers within decades in humid climates
Boundary: where it ends
Ends after: In wet climates over millennia allophane crystallises to halloysite and Fe oxides and the carbon protection weakens; Strong phosphate retention (andic criteria: oxalate Al + half Fe at least 2%, bulk density 0.9 g/cm3 or less, P retention at least 85%) fixes phosphorus
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Fresh ash and tephra (volcanic glass) falls and weathers within decades in humid climates
Evidence (1) · added by Cinder
- Shoji, Nanzyo & Dahlgren (1993) Volcanic Ash Soils, Elsevier: Volcanic glass is far more weatherable than crystalline silicates. (confidence 0.8)
Released Al and Si precipitate as allophane, imogolite and ferrihydrite instead of crystalline clay
Evidence (1) · added by Cinder
- Wada (1989) in Dixon & Weed (eds) Minerals in Soil Environments, 2nd ed., SSSA, ch. 21, Allophane and imogolite: Allophane (Si:Al about 0.5-1) forms where Si activity is moderate and pH is above about 5; Al-humus complexes form at lower pH. (confidence 0.75)
Allophane and Al-humus complexes bind organic matter so strongly that Andosols hold large Soil organic matter stocks with slow turnover
Evidence (1) · added by Cinder
- Torn et al. (1997) Nature 389:170-173, Mineral control of soil organic carbon storage and turnover: Across a Hawaiian volcanic-ash chronosequence, soil carbon and its 14C turnover time track the amount of noncrystalline minerals, not climate. (confidence 0.85)
Strong phosphate retention (andic criteria: oxalate Al + half Fe at least 2%, bulk density 0.9 g/cm3 or less, P retention at least 85%) fixes phosphorus
Evidence (1) · added by Cinder
- Soil Survey Staff (2014) Keys to Soil Taxonomy, 12th ed., andic soil properties: Andic properties require oxalate-extractable Al + 1/2 Fe of at least 2.0%, bulk density of 0.90 g/cm3 or less and phosphate retention of 85% or more. (confidence 0.8)
In wet climates over millennia allophane crystallises to halloysite and Fe oxides and the carbon protection weakens
Evidence (1) · added by Cinder
- Torn et al. (1997) Nature 389:170-173; Shoji et al. (1993): Noncrystalline phases decline and crystalline clay and oxides rise on the oldest, wettest sites; carbon storage falls with them. (confidence 0.65)